Page - (000034) - in Biomedical Chemistry: Current Trends and Developments

1.1.14). This step consists of an electrophilic aromatic substitution, catalysed by DMAT synthase. Scheme 1.1.14: Reaction mechanism for the synthesis of DMAT from tryptophan and dimethylallyl phosphate. 1.4.4 Eliminations Reactions An elimination reaction is a type of reaction upon which there is a net elimination of a molecule from another. To clarify this point, look at the example shown in Scheme 1.1.15. Scheme 1.1.15: Dehydrogenation of ethane to form ethene through two different mechanisms: proton-hydride transfer and a radical mechanism, both leading to the elimination of what is equivalent to a hydrogen molecule (the arrows without origin represent electron transfers to/from other molecules). A dehydrogenation reaction involves the net elimination of a hydrogen molecule, but does not necessarily release a hydrogen molecule. It may proceed through abstraction of a proton connected to one of the carbons followed by transfer of a hydride from the other. It may also follow a radical mechanism by hydrogen atom abstraction from both carbons (Scheme 1.1.15). In a dehydrogenation, the elimination is oxidative because the oxidation state of each carbon atoms goes from -3 to -2, a net molecular change of +2 (Chapter 1.1.4.8). In mechanistic terms, non-oxidative eliminations may occur in